Transducing system to compensate for torsion in a magnetic record wire



July 12, 1949. J. NEUFELD 2,476,110

TRANSDUCING SYSTEM TO COMPENSATE FOR TORSION IN A MAGNETIC RECORD WIRE Filed Sept. 8, 1944 ERASING HEAD REPRODUCING HEAD RECORDING HEAD RING RING MODULATOR MODULATOR Patented July 12, 1949 TRANSDUCING SYSTEM TO COMPENSATE FOR TORSION IN A MAGNETIG RECORD WIRE Ja o eufe ulsa, Ok a,

Application September 8, 1944, Serial No. 553,188

2 C ims- This invention relates to sound r ordin and;

methods of magnet c. re erd n'e ne v in long tu inal mas. at on" inwhiehhe d ecion o maen tiaa e i the tabl maeaeti able m m er" n the eth a n alvlns "per en ular er an ver e ma n tiza ion n wh h" t r c i n f a netizatiQ -is. subs anti lly erpen ar o he a e f themevahle masaetizable membe Se orin ta ee-ifeeund ec rdin masn tiq ape by C- Hickman, Bel-.1 Sy tem ca ournal v0 X a -.21. Ap l 1 37 a- -171.)

ar i t at mp of m g c r co d n er o theongi udinal co d ng t e in Wh =h a magnetizable. member of round cross. section, ame a ire magneti ed, ong t d na y t a v r -Tins de re in accerdan ew th e ur nts of the. that it. wasdesired to record; Al he sh this method w orkabl and od ed seful esult it was d sccwer y a nu oi rkers tha i orde to ch eve h gh u it a ne essa o meth wire t r ati y h h speed. as high s 5 t mi'eetp r e ondme ous efforts were mageto'produce. an instrument at wou d in olve lo r peed o Wir nd n th t. ceanectioa t became a aren at it a necessary to design a co d g a pa atus apable i magnetizing extreme y short section of wire, of the order of only a few thousandths of i ch. Dur g th s re earch W rk i as i ove d, that. even thc sh n y a e y short s on of the w e asexpo ed to a ma ne eld, a somewhat longer section tended to become masaetizeabecause the magnet sm o ld s ead long udinall a ae he wire.- hus. f a mac et c re ord n head as r il th would eis substanti lly arall l: tov

ord so tha on an ext mel smal n f en th of. w re were ex osed to he m g e c fi d. three or four times that length would become ma n t zed Th s phenemenen s identified a ma ne c pr adin In lard r.- to over ome the efi sts o ma eticspreadinsl a m th a i ace d n tran v rse y s de elo ed Transver al reco din ha be n ereto or ascempli h d a steel m' tbc v o tape .....d 425 In hwide havin its ends. secured to suitable winding reels and passing between a pair of recording magnets (see for: instance British Patent 389,117 or the afore-: mentioned paper by C. N. Hickman). The pole pieces of the recording magnets were placed di-.- rectly opposite each other, so that the magnetic pattern consisted of variations in the intensity of magnetization, the direction of the magnetization being. substantiallyperpendicular to the surface of the tape, thus producing a transversemagnetization of the tape. In transverse ma netization the flux in. the tape is in the direction of'its thickness, 1. c. it is perpendicular to. the axis of the movable tape. tape so magnetized may be. thought of asa series of'e-lemental magnets .125 inch wide and. .001. inch long, as contrasted With a. tape longitudinale 1y magnetized by poles spaced alongthe tape.

been substantially eliminated in the transversal magnetic recording upon tape. The method at an e sa ecording on tape has al o. one througha very thorough development, and at the.

present stage the transversal recording on tape. is very much u e ior in the qu l y of eam: duction to thelong-itudinal recording on a thin ffir Whe om arin t e ality t at can be h e ed w th an r o i g o it s im:

portant to comparethe performance for a given speed of the medium on which the record is being made, Qpviou ly, it is possible to record higher;

freguencies by running the apparatus faster, but

at a given speed difierent methods would be capab'le of recording a different range of frequencies, and for purposes of comparing one method to another it is important to keep this in mind.

The best apparatus developed for recording' transversely on steel tape is capable of recording frequencies up to 8000 cycles per second for a tape speed of 1.6 inches per second, .(see the above. referredto article by. C. N. Hickman). Whereas, the most highly developed longitudinal recorder. requires a wire speed of inches per second in order to reproduce frequencies up to 8000 cycles per sec. This represents a very substantial difference, and this clifierence is mainly due to the fact that, in the one case there was no magnetic spreading longitudinally, While in the other case here was.

Despite this large difierence in performance, the magnetic recording apparatus utilizing a thin' wire is receiving a Wide recognition and is ex!- In. other words, a.

3 tremely useful, because the mechanical problems in handling Wire are very much easier to solve than the mechanical problems in handling a steel tape. Wire can be wound upon a spool comparatively easily with little danger of kinking; where as, tape requires special guiding mechanism andhas to be very carefully layerwound; otherwise, kinking and tangling occurs. difliculties, the storage reels on which a steel tape is wound usually are considerably larger than the storage reels on which the same length of wire has been wound. This very much greater mechanical convenience for handling wire as compared to tape or ribbon accounts for the fact that Wire recorders are in use today despite the fact that the performance that can be achieved with wire recorders for a given speed of wire is very much inferior to that that can be achieved with tape recorders forthe same speed of tape. As pointed out above, for a given speed, the wire recorders are about one-fourth as good as the tape recorders. However, the handling of the wire is so much easier and, therefore, this compensates for this factor of four and makes the wire recorder still competitive.

-It is apparent, therefore, that great advantage could be derived from an instrument that would reproducing problem is very much complicated by the fact, that the wire twists, and that at certaintimes during the reproducing process the magnetism on the wire is directed in a direction such, that the pickup device responds very unfavorably. In fact, under certain conditions, the

magnetism in the wire can be oriented accidentally exactly at right angle to the direction for which the reproducing device is set, in which case the reproduction will be completely absent, i. e.,

the pickup device will not respond to the magnetization of the wire and will produce zero Voltage. One of the reasons, in fact, for employing steel tape instead of wire is to prevent the twisting, the steel tape being held mechanically be-" tween proper supports which present it to the reproducing head always in a given orientation. Because of the round cross section of the wire it is not possible to hold the wire always in one position and twisting is absolutely unavoidable.

Numerous efforts have been made to get around this difliculty, but without success, because it is impossible to design a reproducing head that will uniformly respond to the transverse magnetism in the wire, irrespective as to whether the twisting of the wire takes place or not. No matter what kind of a magnetic circuit is employed, there always appears to be an angle in the orientation of the magnetism of the wire at which the reproducing device will give zero response. When the wire twists through the range that comprises this orientation, the reproduction is totally ab sent and only the noise due to the magnetic irregularities of the wire remains.

This invention describes a means for picking up transverse magnetism in the wire irrespective of orientation. The principle consists in providing'a pair of pickup magnetic circuits or coils set at right angles one to another, so that when the voltage picked up by one coil is zero, the voltage picked up by the other ismaximum'. Consequently, one of the pickup coils will at all times be re- .sponsive to the transverse magnetism of the wire,

' irrespective of the orientation of the wire cross Because of these section with respect to the pole pieces of the reproducer. Another feature of this invention consists in the provision of special electronic circuit that will always connect the two pick-up coils in such a manner as to always produce an arith rangement, it is possible to combine all the advantages of recording upon a thin wire, such as ease of handling, cheapness, the general availability of the very long stretches of Wire, etc. with 'all the advantages of recording upon a tape, such as high quality per unit of speed. Consequently,

the present invention represents considerable ad. vantage over the art, because it makes it possible to employ now wire recording and run the wire at a speed of only one-fourth the speed that was necessary previously for the same results.

In accordance with a specific feature of' this invention, the record is made on a very thin slowly moving magnetic wire having high magnetic retentivity employment of transverse magnetization. The transverse magnetization is induced by means of pole pieces contacting or nearly contacting either side of the Wire, the pole pieces being made of laminations of magnetic material of high magnetic permeability, high resistivity and very low retentivity, and being tapered on one end so that the portion adjacent of the desired frequencies, the magnetic recording wire had to be driven at such a high speed that it was not possible to make a continuous recording of a desirable duration on a convenient length of the recording wire or tape.

It is accordingly a primary general object of the present invention to provide a magnetic recording machine and method, in accordance with which a recording of comparatively long duration maybe made on a recording element'of a normal 1 or convenient length.

' Other objects and advantages of the invention, will be apparent from the following specification when taken with the accompanying drawings in which:

Fig. 1 is a diagrammatic view' of a recording and reproducing apparatus showing means for making a record upon a movable wire, means for erasing the record from the wire, and means for effecting the reproduction of speech from the record;

Fig. 2 shows diagrammatically the front and Fig. 3 shows diagrammatically the front and a cross sectional view ofan element of the apparatus that is used for effecting reproduction only.

Fig. 4 shows certain geometrical relationship between. the wire and the pole; piecesor, the: h cording electromagnet: during; the process of; r-e-rcording.

Fig. 5 shows certain geometrical; relationship between the wire and: the. pole pieces oi the.v re: producing electromagnet; duringv the' process ofireproducing.

The apparatus shown in. Fig; 11- is. provided with a. supporting base I., bearing members, 2, and. spools. 3', 4; which are journalledwinv thesebearing: members. Upright guide-members Sandi flITGi-PIQ-a vided and these guidememberssare provided re-. spectively with slots; 1', 8: for the passage; of; the. recording wire. At the commencement ofa re-. cording operation, a spoolof wire. 3:. is. provided; the spools 3, are kept. in stock and are readyfol'; operation. The wire m is; drawn off. of the spoot 3 and wound upon the spool Mby any. suitable. motive power such. as. the-..motor 9: When, the, wire is. passing fro-mthe spool 3: to. be wound; on spool 4, it is drawn through slot T in upright. member 5 and it passesa seriesof electromagnetic: devices. The first electromagnet H is provided for recording magnetically sound uponthe wire and; is. designated as.recordin head. The sec-. ond. electromagnet I2 is provided for reproducing sound: from, the magnetic recordings on the wire,v and is designatedv as reproducing head. Thethird' el'ectromagnet. I3 is. provided: for thepurpose of erasing the magnetic. recordings from the: wire, and is. therefore. designated as erasing head.

In order that a. record: may be erased from the wire, the electromagnet i3 issupplied; with cur-. rent from a source I55 by.- means of conductors. 1.6.. A switch I1. is alsoprovided: to. complete the cir-. cuit at will. When current is supplied to. the electromagnet. l3, the wire passing between the poles is left in a uniform and demagnetized con-.v dition.

The wire H) is moved in. the direction indicated by the arrow, regardless whether a .record is: tobe made or if a record to. be reproduced. For. instance, in cases that almost theentirerecordedi wire has been wound. on the spool 4,. a back -Wind-.. in thereof to the spool: 3 is neoessari-lyrequired before the reproductiono-f this record or records can be, commenced... This ,backwinding is accom-.-. plished by means of a. motor adapted tad-rive the spool 3 through the shaft 21,

The recording head; it consists of: anelectron magnet having an iron. core 24. and a winding-15;. Wound around the core 24, The. core 241is. pros. vided with two. pole pieces. 26; and 21, immediately; adjacent one to another. The pole pieces. are provided with; sharped'gesin form; of. knife blades. in order to localize within, a narrow. zone or .ex-. ploration the flux that .passes between them. The, narrow air gap ween the. p.0 8 piece 26., His d nated by 2.8. The Wire, 10.. is made to pass through the air gap 28 in such a manner, that the axis. ofthe Wire is perpendicular to. the line joining the pole pieces 2.6:.- and 21. The. winding is connected through. the. battery: 30-:to. the sec-... ohd-ary winding of the, transformer 31., the -pri-.. mary Winding 0t which. is connected through the battery 33 and: the switch 34. to the microphone. 35-.

Fig. 2 shows diagrammatically the front view and twov cross. sectional; viewsof, the recording; he d H. n. particul r. Fia, 2A shows the front. view... Fi 2B shows. the crossz s c ion. th u h a. plane passing through the ax of the wireand; perpendic l r t the. line in h.:PQ .Q-Pie6S 82.91 6 passin throughi he axispf the; he. ne inin he: pole-p eces 11:

It is ap ar n that; as thew-ire 0: is moredsia the direction ofthe arrow; as described above, it s rou ht.- t .av ry=-hi htransverse.magnetiaas ti n by t e flux set upr etw nthe po pieces: 26.. 2-1. By transverse magnetization? itis; meantthat: he flux inrthQ-Wi-re; is in the direction firitsa. thickness, i. e. it, is perpendicular tothevaxis; oi: e wiren; other. Word Wire so ma netized; may e ho ht: of as: a. series of elementalnmaa, nets directed .transverselyto the axis; of. the-wire; as. Qon-trasted with; a wire longitudinally.- mag-. netiaed bypoles spacedalong the axisofi the wire.

In, the arrangementdisclosed, the pole tips 26;: 2-], are very close, butnot. actually in CGlitaCUWit the wire, although, in some instancesan actua contact; can be realized. An. appreciable-sepaa rati n Of: the po e tihswill, of course, materially; reduce the efliciency-of the system.

The reproducing, head 112 is shown. diagram-s. matically in, Fig. 3",. In particular, Fig. 3A showsthe front View. of thelreproducing head .and Figs 3B.showsthe cross sectionthrough a, planepassa ing through the Wire I0. and through a line...join mg. the pole. pieces. The reproducin head: I52? consists essentially of a ferromagneticrri-n 40? with four protruding; pole pieces. 4t, 42, 43:, 4'4!- directed towards inside of the ring, and of a thin ferromagnetic diaphragin-z located. in the cen--. tral. portion, of. the ring and rigidly set into the pole pieces M, 42;, 4.3. 44. The diaphragm, pola pieces, and ring are-all: designed to be an intogral unit. The diaphragm 50: is provided-with a' hole 5| just barely-large enough to pass the wire I50; through the diaphragm, and is provided with diagonal cuts 52:, 53 54*, 55; The purpose or the diagonal. cuts is tQ-prQduce a high reluctance path. from one section of the diaphragm to another, and to help guide the. magnetic lines through the pole, pieces, and prevent it from short circuiting by the presence of a, continuous ferromagnetic path. The pole pieces 4|, 42', 43, .are provided with coils 5'6, 51 58, 59-; respectiVaIy; Coils 5.6;, 5.8:.areconnected in series and coils 51;, 5,9; are connected in series. These two pairs of' coils are broughtup to the leadwires; designated as, fill and; 6], respectively.

The outputs derived from the lead: wires 60; 6b are respectively fed into conventional amplifiers 623. 63 through switch'mechan-ism 6d andare .ap-!. plied to the. input terminals of. a. ring modulator contained within the rectangle 66.

The ring modulator is well known in the art' and has been described. in the U. S. Patent No; 2,025,158, issued on, December 24:, 1935,. to. F: A; Cowan, and in; an, article by R. S. Carruthers om Copper ox de. modulators in carrier telephone systems. the Bell Sy tem Technical. Journal, vol: XVIII; .93 pp. 315-331;. The type of the circuit; contained inthe dotted; rectangle 66 is illustrated ii -Fig. 20,, page 31 8, of the said article. The ring modulator is essentially a double balanced. modulater. Bydouble balanced. is meant a modulator: inwhich eachv input is balanced out from the out put, and the output contains therefore only the modulation products. The operation of.:a double balanced modulator shall. be described hereafitert In the ring modulator 66. two currents arrive from the leads 60, 6-! and. are respectively applied: to the input terminals 10a, 10b and Hot, Hb, re. spectively.

It shall appear obvious in the subsequent de-v script-ion, of my invention. that when the ma-...

2.5, 2.1 and Fig. 2Cv shows the oss sectionthrough netized wire I20 during itsmotionin. thedirection:

7 of the arrow, passes through the Opening 51, the coils 56, 58 and 51, 59 will respond to the varying magnetic field derived from the motion of the magnetized wire l and will produce two voltages across the windings of these coils, that are substantially proportional to the rate of change "of the magnetic flux. These two voltages will be derived from each of the pairs of coils 56, 58 and 51, 59 and will be applied across the leads 60 and 6|, respectively. It is apparent, that the magnitude of each of these two voltages will depend upon the orientation of the magnetism of the wire with respect to the pole pieces of the reproducing head l2, and since the wire twists, the magnetism of the wire may be directed in such a manner that one of the two pairs of coils 56, 58 and 51, 59 may respond very unfavorably. In fact, under certain conditions, the magnetism in the wire can be directed accidentally exactly at right angles to the axis of one of the pairs of coils, say to the pair of coils 56, 58. In this case the voltage generated by the coils 56, 58 will be zero because there are no flux linkages between the magnet- 10 flux produced by the wire l0 and the coils 56,

58. However, at the same instant, the flux linkages between the magnetic flux produced by the wire In and the coils '1, 59 is at maximum, because the magnetism of the Wire will have the same direction as the axis of the coils 51, 59. Consequently, the voltage generated by the coils 51, 59 will be maximum. It is therefore apparent, that, because of the twisting of the wire, the magnitude of the response of the coils 56, 58 and 51, 59 will continually vary and at any instant will be dependent upon the orientation. of the magnetism of the wire with respect to the axis of the coils 56, 58 and 57, 59. Consequently, the two voltages derived from the coils 56, 58 and 51, 59 will be applied across the leads 6!! and 6|, respectively, and will have magnitudes depending upon the orientation of the magnetization of the wire (representing the speech signals) with respect to the axis of the coils 56, 58 and 51', 59, respectively. More particularly, each of these two voltages will have a magnitude representing the directional component of the speech signals impressed magnetically upon the wire I0, the said directional component being referred to the axial direction of the coils 56, 58 and 51, 59 respectively.

Consequently, we obtain across the leads 60 and' Bi, respectively, two voltages, each of said voltages representing the response of the corresponding pair of coils (56, 58 or 51, 59) to the varying magnetic field derived from the motion of the magnetized wire it]. It is apparent, that each of these two voltages will represent the facsimile of the speech signals impressed magnetically upon the wire and, consequently, these two voltages will vary with respect to time in a substantially similar manner. The only difference between the voltages across the leads 60 and 6!, is the difference in intensity, since the intensity depends upon the orientation of the magnetism of;

the wire with respect to the axis of the coils 56, 58 and 57, 59, and because of the twisting of the wire, this orientation varies.

If, for instance, the orientation of the magnetism of the wire i ll is such as to make an angle of 45 degrees with the axis of the coils 56, 58, and 45 degrees with the axis of the coils 51, 59, then the signals derived from the leads 6!] and 6! are equal in intensity. If, however, the orientation of the magnetism of the wire I0 is such as to make a smaller angle with the axis of the coils 56, 58, than with the axis of the coils 51, 58,'the signal shown in the figure, the voltage derived from the leads 60 is applied acrossthe input terminals 10a, 10b of the modulator, and the voltage derived from the leads 6! is applied across the input terminals Ha, 1 lb of the modulator. It is apparent, that the two input voltages applied across the terminals Illa, 10b and Na, Mb represent the facsimile of the same speech signaland may differ one from another in intensity. It is also apparent that these two voltages may be applied to said terminals either in phase coincidence or in phase opposition, depending upon the orientation ofthe magnetism of the wire l9 with respect to the pole pieces of the reproducing head l2. Because of the twisting motion of thewire ill, the orientation of the magnetism continually= changes,- and consequently, 'as' the reproducing process proceeds, the two input voltages applied to the modulator 66 are eitherin'phas'e or in opposition. In'thejfurther description of myinvention, I shall explainmore in detail the geometri-' cal relationships involved betweenthe direction of magnetization of the signal impressedupon the wire and the orientation of" the pole pieces of the reproducing head [2, and will show the particular orientations occurring during the twisting of the wire that shall .correspondfto the phase reversalof the'input-voltages of the modulator 66.

These geometrical relationshipsshall be explained in'connection-with Fig. 5.-

As is well known, one of the modulation products' produced in the modulator 66 is the difference between the frequencies of theztwo applied input signals. In this case, however,.the two signals have-the same frequency, and consequently,

the modulation product is a component having zero frequency and is therefore represented by a direct current. The polarity of this direct current depends upon the phase between the two signals supplied to the modulator 66 from the leads 66 and the leads 6!, Assume that in the circuit shown the outputs of leads 66 and iii are in phase. Then the output of the ring modulator circuit 66 will have a D. C. component such, that the polarity is so as to make the output terminal 16a positive and the terminal 161) negative. It is apparent, that when'the phase between the voltages applied across input terminals ma, 78b and H a, 'Hb is reversed, the polarity of the voltage appearing between the terminals 76a and 161) will be reversed, i. e., 16a will be negative and 16b will be positive.

Consequently, we shall obtain across the out put terminals 16a, 16b of the ring modulator 66 a D. C. Voltage the polarity of which will depend upon the orientation of the magnetism; wire with respect to the pole pieces of the repro-l ducing head l2. Furthermore, during the reproducing process the twisting of the wire will cause a change in the orientation, and consequently,

the polarity of the voltage across the output I 7Ia, ITIb of another ring modulator 166 in conventional fashion. The ring modulator 1 66 is structually similar to the ring modulator 66, and the numerals designating various elements of the modulator I66 differ from thenumerals designating the elements that are analogous in their functional performance in the modulator 66 by the numeral I00. Thus, for instance, in the modulator I66 the input terminals I' IBa, Il'Ob correspond to the input terminals 111a, "'I'nb in the modulator 66. Or, the rectifier bridge in the -modulator I66 consists of rectifiers I8-I, I82, I83, 184, whereas the corresponding rectifiers in the modulator 66 are designated by numerals BI, 82, $3, and 84.

It is apparent, that voltage appearing across the output terminals IIta, IIBb of the modulator 166 represents the modulation product of the respect-ive input voltages applied across the terminals I10a, Hub and Illa, IT-I-b, respectively. It is noted, that the voltage derived from the leads 6D is applied after amplification in the amplifier 62 through the leads 253 and the transformer "251 to the input terminals 11 a, 11 0b, and the D. C. voltage derived form the output of the modulator 616 is applied to the input terminals Illa, -'-I'-'llb. Consequently, the output voltage derived from the terminals 116a, 11 6b represents substantially the product of the two input voltages.

it is of particular interest to note in this connection, that one of the input voltages applied to the modulator i 66, namely the one applied across the terminals I'll-a, IFH b, is always an C. voltage, the polarity of which varies in response to the twisting motion of wire ill. The other input voltage applied across the terminals 11 0a, ill-11b represents the signal induced by the moving wire in cells 57., 59 :and is derived from the leads $11. It is apparent, that the output voltage derived from the terminals I 'lfia, I'I-tb represents the product of the two input voltages. Since this case one of the inputs is represented by a D. :C. voltage, the output will he substantially similar to the input voltage derived *from the leads :60; however, the polarity of this output voltage will vary in direct relationship to the polarity of the input voltage applied across the [terminals Ilia, =lz'lzlrb. Consequently, the output voltage derived from the terminals 'I' I Ba, *Htb of .the modulator 166 represents at any instant the signal induced kry'the moving wire in coils 51, 59 and the phase of this voltage will vary in response to the twisting motion of the wire -I0. In particular, there will be a reversal in phase of the output voltage :at .any instant at which the twisting motion :of the wire causes the reversal :of polarity of iihe D. t). voltage applied across the input terminals :I-TrIu, 111 b.

Consequentlm 'for direct :current applied across the terminals ';I'I;EI.a, iIeIIib .the vring modulator .I66

acts 28.813, reversingswitch, the reversals 01" which are determined by the changes "in polarity of the voltage applied across the terminals I' I'I'a, Hill).

Therefore, when the terminal ll'l la is positive withrespect-to the :termi-nal I I! I b, the ring =modulator 166 ,makes a straight through connection between the input terminals tl'flIla, .IWband the output terminals I'ltafllilfib. onithe other hand, when the polarityzof the terminal I'Ha is negative with respect to the terminal 'I'Tlb, the ring modulator I66 provides a reverse connection between the input terminals zI-Tfl'a, .sIl'IIlb and the output terminals ;I;-'I.6a, ':I 161).

' .The object :of .my invention consists in deriving the two voltages from the leads 60, BI and adding them in such a manner that the resultant voltage is larger than any of the two component voltages derived from leads 6!] and 6|, respectively. Consequently, both component voltages should be arranged in series one with respect to another and have their polarities arranged in such a manner as to he in phase one with respect to the other. It is, however, apparent that the phase relationship between the voltages derived irom'leads 6D and 61, respectively, depends upon the twisting motion of the wire ID, i. e. there are some orientations of the wire magnetism with respect to the pole pieces of the reproducer I2, tor which the voltages derived from leads 6D and '61, respectively, are in phase, and there are other orientations of the wire magnetism, for which these two voltages are in phase opposition. Therefore, I am employing the ring modulator I66 as a reversing switch in order to reverse the phase of the voltage derived arom leads 513 for certain orientations of the wire II) in such a manner that, irrespective of the twisting motion of the wire I B, the two voltages derived from leads 6!] and BI, respectively, will always add together in a complete phase coincidence, so as to produce :a resultant voltage that is larger than either of the two component voltages,

Referring now again :to Fig. 1, it is seen that the input to the ring modulator M66 is supplied by part of the current derived from the leads 6-0., and the output :of ring modulator II 66 is applied through the transiormer 2010. Thesecond- :a-r-y winding of the transformer :mm is provided with two terminals 2! and 2022. The terminal 202 is connected through the lead 2113 to one of the :utput terminals of the amplifier '63, while the other terminal of the amplifier 63 is con-- *nected through the lead 204 to the terminal 205. Consequently, across {the terminals 200, 205 there appears a voltage that represents the sum of the output of the amplifier '63 and :of the output of (the modulator I65.

:It is therefore apparent, that the voltage derived from the terminals 2110, 12.05 consists of a signal "supplied :by the output :of the amplifier 63 connected in series with signal supplied from the output of the amplifier :62 and transmitted through the ring modulator @I 66 which acts as a reversing switch. The phasing of the whole circuit is adjusted so that, when the outputs of the amplifiers :62 and 153 are in phase the ring modulator .Ifi66 is polarized in such a way as to provide .a straight through connection and, at the terminals 200, 205 appears therefore a signal representing the sum of voltages supplied 'by the leads 1'60 and J6]. Furthermore, when the wire I-IJ twists, and .as a result of that the phase "between the voltages derived from the leads 6|] and '61 reverses, the ring modulator 66 provides a polarizing voltage to the ring modulator 166 of such a polarity that the connections are reversed and again the voltage derived from the terminals .200, 205 represents the arithmetic sum of the voltages supplied by leads and Gil respectively.

'It is apparent, that when the device is in operation, the coils '57, 59 and 56, 58 are arranged to respond continuously to the magnetism of the wire and to produce the two component voltages applied to leads -60 and "61, respectively. It is also apparent, that as the wire twists, there are some orientations of the magnetism of the wire which cause either of the two component signals to be zero. There is, however, no orientation of the magnetism of the wire 'I'II which would cause both component signals to be zero simultaneously, since at the instant when one component signal is zero, the other is maximum. Consequently, the sum of the two component signals represented by the voltage across the terminals 209, 295 can never be zero. The two component signals are arranged to respond in such a manner so as to aid each other continuously. As the wire twists, the orientation of the magnetism changes automatically, and, under such conditions, the two components that are picked up by the pick-up device are both utilized and combined in the proper polarity to aid one another continuously. Furthermore, it is apparent, that the instant of the automatic switching action by means of the ring modulator coincides with the instant when either of the pairs of coils 56, 58 and 51. 59 supplies zero voltage. Consequently, the switching operation is noiseless and free from external disturbances.

Consider now more in detail the operation of the arrangement of Fig. 1, as a recorder and as a reproducer. The operation is controlled by three switch units designated by numerals I1, 34 and 64. When it is desired to impress sound upon the wire 10, the switch IT controlling the erasing head I3 and the switch 64 controlling the reproducing head 12 are open, and the switch 34 controlling the recording head II is closed. The wire is assumed to be wound upon the spool 4 and the motion of the wire in the direction indicated by the arrow is being produced by unwinding the wire from the spool 3 and winding it upon the spool 4. Sound waves are arranged to impinge upon the diaphragm of the microphone 35 and cause motions in the electrodynamie transduoing mechanism which generate electrical currents that are representative of the sound waves. The speech currents are transmitted through the transformer 3| to the winding 25 and produce in the air gap 28 separating the pole pieces 26, 21 a magnetic flux which is a reasonably exact facsimile of the sound waves that impinge upon the diaphragm of the microphone 35. Be-

fore the wire enters into the air gap 28, it is assumed to be in demagnetized condition. It is ap parent, that an extremely small portion of the wire which at a given instant is in the direct neighborhood of the pole pieces 25, 21, becomes magnetized in the direction perpendicular to the axis of the wire and to the extent dependent upon the strength of the magnetic flux at the instant under consideration. Therefore, after this portion of wire has left the air gap and proceeds in the direction of the arrow towards the spool 4, a subsequent portion of the wire enters the air gap and becomes subsequently magnetized in the direction perpendicular to the axis of the wire and to the extent dependent upon the strength of the magnetic field in the air gap at said subsequent instant. Because of the magnetic retentivity, each element of wire, after having passed through the air gap acquires a magnetic moment which is vectorially located in a plane perpendicular to the axis of the wire and the direction of which is determined by the position of the pole pieces 25, 21 with respect to the cross section of the elemental wire at the instant it was subjected to the magnetic field. The geometricrelationship showing the direction of the magnetic force with respect to the position of the pole pieces and the cross section of the wire at the instant of magnetization is shown in Fig. 4.

It is therefore apparent, that as the wire I moves in the direction of the arrow and becomes wound upon the drum 4, it acquires and retains a succession of magnetic moments directed transversely to the length of the wire and representing the speech currents applied to the air gap 28. In order to reproduce the speech thus stored upon the wire, a back Winding upon the spool 3 is necessary by means of the motor 20. Subsequently, the wire is being moved again in the direction of the arrow and the unwinding motion of the drum 3 recommences.

We shall show at present that the magnetic structure represented by the head I I can be used for recording of signals only, and cannot be used for the reproduction of the magnetic impressions from the moving wire Hi. It is apparent, that when the magnetized section of the wire passes again through the air gap 28 of the electromagnet II, the relative position of the retained magnetic moment with respect to the pole pieces 26, 21

is not any more the same as shown in Fig. 4A.-

Because of the twisting of the wire during its windin and unwinding motion, the cross section of the element of the wire that repass'esthrough the air gap 28 does not occupy an identical position to the one during the instant of mag-'- netization. The direction of the magnetic moment vector is usually inclined with respect to the axis joining the pole pieces by an angle that may be designated as a as illustrated in Fig. 43. Consequently, the amount of flux interlinking with the coil 25 that is caused by the magnetic moment of the elemental wire depends upon the value 0:, where 11 indicates the relative value of twist, i. e. the change in angular displacement of r the elemental section of wire at the instant it repasses through the air gap 28 as compared to the reference value of the angular displacement of the same section of wire at the instant at which the magnetic impression was made. When a=0 or when =180, the magnetic flux derived from the Wire and interlinking with the coil 25 is maximum, when a= or a=270, this flux is zero, and for any intermediate values of a this flux is between a maximum and zero. Consequently, the electromagnet I I cannot be used for purposes of reproducin the signal impressed magnetically upon the moving wire 10, since, for some angular positions caused by the twisting of the wire there is no flux interlinking with the electromagnet l l, and, therefore, the electromagnet does not respond at all to the signal impressed upon the wire.

Therefore, in order to reproduce the signal impressed magnetically upon th moving wire IO, the switch 34 is open in order to render the recording head ll inoperative, and the switch 64 is closed thus permitting the magnetized wire to energize the reproducing head l2.

The reproducing head l2 consists of two pairs of pole pieces 4|, 43 and 42, 44 arranged at 90 degrees one with respect to another. Consider now the succeeding elemental sections of wire that traverse the opening 5| of the ferromagnetic diaphragm 50 of the reproducing head. Each of these sections will act as a small magnet and will supply a magnetic flux traversing the diaphragm 50, the pole pieces and the circular ring 40. It is therefore apparent, that the pair of pole pieces 4|, 43 and the pair of pole pieces 42, 44 will each supply a convenient magnetic path for the changing flux resulting from the passage of the magnetized wire, and cause this flux to interlink with the associated coils. This changing flux generates two voltages in the pair of coils 56, 58 and in the pair of coils 51, 59,

respectively, the magnitudes of these voltages depending upon th interlinking of the magnetic flux caused by themoving wireiand the associated coils. Assume a more specific'case in which the wire 10 passes through "the hole of the reproducing head. .Let the relative position that the cross section of the wire occupies with respect to the pole pieces be the one shown in Fig.5. As shown in Fig. 5, themagnetic vector of the elemental section of the wire'has 'a direction represented by an arrow Aand forms an angle B with the line joining the pole pieces- 41, 43 and angle (90fi) with the line joining the pole pieces 42, 44. It is apparent, that when 5:0 or e=1so-tne magnetic flux createdtby the wire and interlinking with the coils 56, :58 is maximum whereas the magnetic flux interlinking with the 'coils 5?, 59 is vzero. On the other hand, when c=90 or 5:270 the magnetic Iilux interlinking with the coils 56, 58 is zero andthe magnetic flux interlinking with the coils .51, 59 is maximum. For intermediate values of B the magnetic flux interlinking with coils 56, '58 is proportional to cos B and the magnetic flux interlinking with the coils '51, 59 is proportionalto sin [3.

The essential and fundamental feature of my invention consists in deriving by means of the reproducer [2 a signal that is substantially proportional to the magnitude of the magnetic efiect stored in the elemental section of the wire, and that is substantially independent of the angle B. Such a signal is represented by the voltage 'derived from the terminals 2m, 2115, and it represents the result of the arithmetical addition of the two pick-up voltages that are derived from the coils 51, 58 and "56, 53, and that 'are applied across the leads 6% and ti, respectively. Byan arithmetical addition I understand the addition in which both pick-up voltages aid each other, i. e. theyare assumed to be always positive as if they were always aligned in phase. Whereas, in an algebraic addition the reversal of phase of one of the pick-up voltages changes the value of the sum, in an arithmetical addition the sum remains unchanged, because both pick-up voltages are made always to be positive,'irrespective of their phase relationships and irrespective of their phase reversals. Consequently, in an arithmetical addition I am adding absolute magnitudes K1 cos Bi-l-Ki sin 61 where K1 cos {31 represents substantially the contribution picked up by the coils/56, "58 and derived from the leads 6!, whereas K1 sin 51 represents substantially the contribution picked up by "the coils 5?, 59 and derived from the leads 6!]. It is apparent that for 5:90" the contribution derived from the leads 56,58 is zero, whereas the contribution derived from leads 57, 59 is K1, and consequently, the composite voltage is equal to K1. If B is larger than 90 and is equal to, say, 90", then the contribution picked up by the coils Then the polarizing 5 56, 58=and zderived from the leads 6l is-equal to -.K1 cos '52 (note the reversal of sign) whereas the contribution .picked up by the coils 51, 59 and derived from the leads 6!] is equal to K1 sin 52. Under these conditions the voltages derived from leads 60, 6|, respectively, are in phase opposition. Then the polarizing voltage derived from theimodulatoraiiii is such as to render bymeans of the:modulator 66 a reversed connection for the voltage derived from leads 6!], and subsequently, both voltages derived .from leads "60 and 61 are added, and'provided'across the'terminals 2!, 205 a :composite voltage that is substantially equal to K1 cos I,62+K1 sin 62 :Assume now, that initially, the orientation of the wire corresponded'to [3 61. Then, as the wire progressed in the direction of the arrow,-it underwent'atwisting motion, and'therefore assumed an orientation B=90 and a subsequent orientation [3='9l)+,62. Assume also, for the'purposestof simplification of our reasoning, that the signal impressed upon the wire had a constant intensity that :did rnot vary with time and that corresponded to the value K1.

.Then "the voltage derived from the terminals 2M, 2% hadan lIlltlQl"./2l1ll6K1 cos fi1+=K1sin fir which "became subsequently "changed to the value Krandfinally became K1 cos 52+K1 sin 82. "We may therefore state that, for any orientation that .may occur during the twisting motion of the'wire the value of .the voltage is where 13 may have 'any'value between 0 and909. By inspecting this formula it becomes apparent that the output voltage derived from the terminals-21H, 285 can never be Zero. It is always contained between a minimum value of K1 (corresponding "to :,8:0) and a maximum value of 1.41 K1 (corresponding to B=45) 'The' wire may, of course, be operated at various speeds'ibymerely' varying the speed of the driving motorzinany-eonvenient manner. One notable feature of this system, however, is the slowness with Whichithe wire can be operated to give satisfactory quality. .At eight'inohes per second or even less, speech is not onlyintelligible but also of a very good natural quality and quite satisfactory for :most purposes. For recording music or other sounds involving higher 'f-requencies,"a somewhat greater speed is desirable, if high quality is required.

"The following'paragraphs shall illustrate the mannerin'which the two input'volt-ages influence the outputvoltage of the modulator 61", i. e. it shall'beshown that when the two'input voltages are in phase, the polarity of the .output voltage is positive, and whenthey are out of phase, the polarity is negative.

Consider now the ring modulator circuit contained 'in the rectangletfi. The circuit shown therein comprises a bridge circuit consisting of four 'rectifiers 8!, E82, '83, M, each of the said rectifiers constituting a separate arm of the bridge circuit and arrange so that the current can flow-only in an anticlockwise direction. The upper cornerof the bridge and the lower corner of the bridge '56 are respectively connected to the input terminals 70b, l'lla and are also connected--'one to another by means of equal =resistances Bl and 88 in series. The other corners of the bridge 89, 90 are respectively connected to the output terminals Mia, Nib, and are also con- 'nected one to another by a pair of equal resistances 9|, 92 in series. The other input terminals Ha, Nb of the ring modulator are respectively connected to the point 93 connecting the resistances 81, 88 and to the point 94 connecting the resistances -9 92.

With the circuit as described, current derived from the terminals 19a, 19b may flow either through the rectifiers 82, 83 or through the rectifiers 84, 8| depending upon its direction, but it can never fiow through all the four rectifiers at the same time, since the rectifiers 82, 83 on one hand and the rectifiers '84, 8| n the other hand are arranged to flow in opposite directions.

Suppose now, for purpose of illustration, that the voltage derived from the terminals Ha, llb and the unbalance voltage derived from the terminals 19a, 79b are simultaneously applied, and suppose that both voltages are in phase, i. e., the terminal b becomes positive as compared to the terminal 19a and at the same time the terminal I la becomes positive as compared to the terminal I lb. Then one partof the current tends to flow from the terminal Ha to the terminal 93 and through the resistor 81 to the terminal 85 and then through the rectifier 82 and through the resistor 9| back to the terminal Mb. The other part of the current tends to flow from the terminal Ha to the terminal 93 and through the resistor 88 back to the terminal 86 and through the rectifier 84 and through the resistor 92 back to the terminal Mb. The currents flowing through the resistors 9|, 92 are equal and of opposite directions. 1

It is apparent that, under the conditions described in the preceding paragraph, the polarity of the terminals 65, '86 will be positive with re spect to the polarity of the terminals 99, 89. Consequently, positive voltages are applied to rectifiers 92, 84. Therefore, these rectifiers will lose their ability of rectifying currents, and will allow currents to traverse them in both directions. At the same time, negative voltages are applied to the rectifiers 8|, 83. Consequently, the rectifiers 8!, 83 will retain their rectifying ability and will block currents attempting to traverse them in the negative direction. Therefore, the rectifiers 82 and 94 are conductive in both directions, and consequently, when the unbalance voltage is being developed across the terminals 70b, 79a, we find that a current tends to pass from the terminal 195 to the terminal 85 and then through the rectifier 82 through the resistors 9! and 92 to the terminal 99 then through the rectifier 84 back to the terminal 10a. This current superposes itself upon the current which is already flowing through the resistors 9| and 92 and consequently the resultant current passing through the resistor 9| becomes larger than the current passing through the resistor 92; consequently, the balancing that existed before is offset because there is a situation where the current flow through the resistor 9| is increased as compared to the current flow through the resistor 92. Thus the voltage drop across the resistor 9| becomes greater and a positive overall voltage is developed across the terminals 76a, 7%. It can be also readily seen that when the unbalance voltage applied across the terminals 191), 70a increases in magnitude the corresponding resultant voltage obtained across the output terminals 16a, 16b increases in magnitude also.

It can be shown, that if the polarity of the first input voltage would reverse with respect to the second input voltage, 1. e., if We suppose that the terminal Ha becomes positive as compared to the terminal Nb and the terminal 195 becomes negative as compared to the terminal 1911, then the balance becomes ofiset in the opposite direction, because there is a situation where the current flow through the resistor 92 is increased as compared to the current flow through the resistor 9|. Then the voltage drop across the resistor 9| becomes smaller as compared to the, drop across the resistor 92 and the overall volt-i age developed across the output terminals 1 611,} has a polarity opposite to the case described above.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. In a magnetic reproducing device for reproducing signals impressed magnetically upon a moving wire substantially transversally to said wire, said wire producing in its neighborhood a magnetic field that varies longitudinally in accordance with said signal and simultaneously varies as a function of the angular position of the wire, means responsive to the magnetic field as it moves in the neighborhood of a fixed point for developing two signals respectively representative of angularly displaced portions of the magnetic field at said fixed point, an electrical transducer, and a switching element inserted between said means and said transducer for variably connecting said means to said transducer.

2. In a magnetic reproducing device for reproducing signals impressed magnetically upon a moving wire substantially transversally to said wire, said wire producing in its neighborhood a magnetic field that varies longitudinally in accordance with said signal and simultaneously varies as a function of the angular position of the wire, means responsive to the magnetic field as it moves in the neighborhood of a fixed point for developing two signals respectively representative of angularly displaced portions of the magnetic field at said fixed point, an electrical transducer, 9. switching element inserted between said means and said transducer for variably connecting said means to said transducer, and means responsive to said signals for controlling said switching element.

JACOB NEUFELD.

REFERENCES CITED I The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 902,773 Stuart Nov. 3, 1908 1,949,409 Cohen Mar. 6, 1934 1,993,616 Nakken Mar. 5, 1935 2,025,158 Cowan Dec. 24, 1935 2,086,601 Caruthers July 13,1937 2,136,606 Bendel Nov. 15, 1933 2,272,821 Roys Feb. 10, 1942 FOREIGN PATENTS Number Country Date 479,468 Great Britain Feb. 7, 1938 

